The present invention relates to a process for polymerizing vinylidene aromatic monomers, such as styrene, to produce polymers having a high degree of syndiotacticity using cationic Group 4 metal catalysts wherein the metal is in the +3 oxidation state. Such polymers may be usefully employed in the preparation of solid objects and articles such as a moldings, films, sheets and foamed objects by molding, casting or the like process.
In U.S. Pat. No. 4,680,353 there is disclosed a process for the preparation of polymers of vinylidene aromatic monomers having a stereoregular structure of high syndiotacticity, by the use of Group 4 metal coordination catalysts in the +4 oxidation state and an aluminoxane cocatalyst.
In U.S. Pat. No. 5,066,741 there are disclosed certain cationic metal compounds formed by reacting certain Group 4 metal complexes including both +3 and +4 metal complexes with ammonium or phosphonium salts of Bronsted acids containing a non-coordinating compatible anion or with cationic oxidizers containing a non-coordinating compatible anion are disclosed. The complexes are usefully employed as catalysts in the polymerization of polymers of vinylidene aromatic monomers having a stereoregular structure of high syndiotacticity.
In U.S. Ser. No. 08/008,003, filed Jan. 21, 1993, now U.S. Pat. No. 5,374,696 certain stabilized Group 4 metal complexes wherein the metal is in the +3 oxidation state and their use as addition polymerization catalysts are disclosed.
Finally in EP-A-493678 (having a priority based on JP 415574/90), processes for syndiotactic polystyrene using certain additional cationic metal compounds formed by reacting Group 4 metal alkoxides or similar complexes in the +4 oxidation state, alkylating agents and cation forming activating cocatalysts (including ammonium or phosphonium salts of Bronsted acids or cationic oxidizers containing a non-coordinating compatible anions) are disclosed.
For the teachings contained therein, the aforementioned U.S. Pat. Nos. 4,680,353 and 5,066,741, U.S. Ser. No. 08/008,003 and EP-A-493678 are herein incorporated in their entirety by reference thereto.